This article explores the school context of tracking, with a mention of the societal contexts of tracking. A brief review of tracking practices, assumptions, and evidence of effects is included in the beginning of the paper. Several relationships within the schooling context of tracking are discussed: (1) student characteristics and track placement; (2) track systems and track placements; (3) track systems, student placements, and learning opportunities; and (4) responses, outcomes, and future placements. Throughout the article, a set of hypotheses is raised to account for tracking's effects and its persistence as school practice. These hypotheses are as follows: (1) the schooling context of tracking consists of a complex set of relationships among structures and events within schools, and this schooling context has long-term consequences for students' cognitive and affective outcomes; (2) the societal context of tracking--specifically, historically grounded assumptions and shared norms about how schools should respond to student diversity--shapes the content and processes of school tracking; and (3) contextual considerations can explain tracking's persistence in schools despite empirical evidence against its effectiveness. Extensive references are included. (SI)